Treatment of plastic materials



Patented Jan. 9, .1945

F PLASTIC MATERIALS William Horback, Newark, and Walter Dempsey Paist, Orange, N. .L, assignors to Celanese Corporation of America, a corporation of Delaware No Drawing. Application December 8, 1942, Serial No. 468,254

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This invention relates'to the treatment of plastic materials, and relates moreparticularly to the treatment of plastic materials made 'of or containing esters of cellulose for the purpose of producing ornamental or other desired effects there- It is an important object of our invention to provide a novel process for producing ornamental or other desired effects in or on plastic materials made of or containing esters of cellulose by an etching operation.

Another object of our invention is the Provision of a novel etching solution for use on plastic materials made of or containing esters of cellulose in order to obtain desired'etched effects.

Other objects of our invention will appear fro the following detailed. description.

Attempts to etch plastic materials having a basis of esters of cellulose have produced unsatisfactory results for the; reason that the etching fluid tried, such as concentrated acetic acid,

,efiected a vigorous dissolving and polishing action, while others, such as caustic soda, chromic acid, hydrochloric acid and nitric acid caused swelling or decomposition of the ester of cellulose material without any etching.

We have now discovered that ester of cellulose plastic material may be etched satisfactorily by using a dilute solution of sulphuric acid, 1. e. an acid solution 'of a concentration of from 25 to 75% by volume and immersing the plastic material in a bath of said solution'for from one minute to one hour depending upon the concentration and temperature of theetching, solution and upon the degree of etch desired. While etching of the plastic material may be obtained by employing solutions of sulphuric acid of a concentration below 25% by volume, the process requires too long a time and is, therefore, commercially uneconomical. We have found that optimum results are obtained by using a sulphuric acid solution of a concentration of 50% by volume. The sulphuric acid solution may be brought down to the desired concentration not only by the use of water but also by the use of other substances such as, for example, borlc acid, phosphoric acid, etc. Such a solution produces an etching on ester of cellulose plastic materials of any desired depth in a relatively short space of time without the necessity of employing very high temperatures.

We have also discoreved that the presence of small amounts of water-soluble plasticizers,

solvents or diluents for the ester of cellulose of the plastic being treated, either in the plastic material or in the acid etching solution, accelerates the etching process. Examples of such water-soluble plasticizers and solvents are diacetin, diethyl tartrate, methyl ce1loso1ve-- acetate, triethylene glycol, dioxan, acetone, alcohol, etc. Any suitable amount of the foregoing accelerating agents may be incorporated in the plastic or in the acid etching solution,

amounts of from 1 to 10% by weight being found to be suitable.

While plastic materials having a basis of any ester of cellulose, with or without the usual well known plasticizers, may be etched in accordance with our invention, we prefer to use a plastic material having a basis of cellulose acetate for preparing the desired etched articles, and particularly cellulose acetate containing plasticizer therefor. Examples of other esters of cellulose which may be employed as the basis of the plastic material to be etched are cellulose nitrate, cellu lose proplonate, cellulose butyrate, cellulose acetate-propionate, and cellulose acetate-butyrate.

Merely by way of illustration and without limiting our invention thereto, the following specific example is given:

- Example A sheet of plastic material of thefollowing is printed in desired design with a resist com prislng, for example, a linseed oil base containing either carbon black, pitch or asphaltum. The resist is then permitted to dry or positively dried by the use of an infra-red lamp. The sheet is then immersed for 15 minutes in a bath of sulphuric acid of a concentration of 50% by volume, the bath being at a temperature of 50 to C. The sheet is then washed free of etching solution with slightly alkaline or plain water and dried. It is found that a sharp etching having depth of 0.004 inches is produced on the sheet. If desired, the etched part is painted or suitably coated to produce a color contrast with the unetched part, as for. nameplate purposes.

The process of our invention may be employed to produce articles of utility and ornamental ar-' acid, such" as compositions containing parafiin, may be used. A plastic composition which is resistant to the reaction of sulphuric acid may also be used asa resist.

Moreover, plastic materials may "be made with heterogeneous or varT-colore'd plastic laminae or inlays, vertically or horizontally composited, some of which laminae or inlays can be etched by the etching solution of our invention and some of whichare resistant, such as polystyrene-ethyl cellulose, Vinylite, Saran, etc. In this way a selective action can be obtained to produce various permanent color-contrast effects. For example, a thin white sheet, say, .005" thick, of

cellulose acetate plastic can be suitably laminated to a black sheet of ethyl cellulose, polystyrene, etc. to serve as a background; The top cellulose acetate sheet, which has been resist-inked with a certain design or lettering is then etched to a depth to expose the bottom or black background layer of ethyl cellulose, polystyrene, etc.

Inasmuch as'the cellulose acetate layer is the have to be visibly controlled to the required depth.

Metal foil interlayers also produce novel decorative eiiects as well as pearl, fluorescent or phosphorescent laminated plastics. Novel signs could be made, for example, in which a facsimile, signature, design, etc. would luminesce in the dark. These signs would be more permanent than surface coated ones. The plastic article after etching can be dipped in acetone to produce an overall polished effect. Here again depending on the solvent used and the character of the plastic interlayers, inlays, etc. contrasting polished and matte effects can be obtained. It is also possible to dip the etched article in a series of dye solutions which are selectively absorbed by the-various plastic layers or parts used so as to produce color-contrasts in the etched and unetched'portions. Furthermore, it is also possible by our invention to printa lace or filigree design on thin sheet material and then subject it to the action I of the etching solution whereby the acid willeat" through the unprinted portion to produce a fine lace 'efiect suitable for doilies, table mats, etc. a

It is 'to be .understood that the foregoing detailed description is given merely by way of illustration and that many. variations may be made therein without departing fromthe spirit of our invention. I

Having described our invention, what we desire to secure by Letters Patent is: v

1. Process for the production of ornamental and other eiiects on plastic material, whichcomprises subjecting plastic material made of or containing an organic acid ester of cellulose to the action 'of anetching bath comprising a sulphuric acid solution of a concentration'irom 25 to 75% by volume.

2. Process for the production of ornamental and other effects on plastic material, which comprises subjecting plastic material made of or containing cellulose acetate to the action of anetching bath-comprising a sulphuric acid solution of a concentration from 25 to 75% by volume.

3. Process for the production of ornamental and other efiects on plastic material, which comprises subjecting plastic material made of or containing cellulose acetate to theaction of an etching bath comprising a sulphuric acid solution of a concentration of 50% by volume.

4. Process for the production of ornamental and other effects on plastic material, which comprises immersing the plastic material made of or containing cellulose acetate and having a resist thereon, for 15 minutes, in an etching bath comprisin a sulphuric acid'solution of 50% concentration by volume, said etching bath being at a temperature of 50 to 75 C.

5. Process for the production of ornamental and other effects on plastic material, which come prises immersing the plastic material having a basis of cellulose acetate containing diethyl t as accelerating agent, said etching bath being at phthalate and triphenyl phosphate and having a resist thereon, for 15 minutes, in an etching bath comprising a sulphuric acid solution of 50% concentration by volume, said etching bath being at a temperature of 50 to C. p

6. Process for the production of ornamental and other effects on plastic material, which comprises immersing the plastic material having a basis of cellulose acetate containing diethyl phthalate and triphenyl phosphate and having a resist thereon, for 15 minutes, in an etching bath comprising a sulphuric acid solution of 50% concentration by volume and containing a water soluble plasticizer or solvent for the cellulose acetate a temperature 'of 50 to 75 C. WILLIAM HORBACK. WALTER DEMPSEY PAIST. 

